This project is superimposed on an ongoing research project funded by NSF concerning cognitive changes over the life-span. The problem addressed is the potential uninterpretability of much cognitive aging literature due to subject attrition. Most studies use volunteers in their older groups. We have found that, in a carefully targeted population, less than 20 percent are willing to serve in a 2-hour experiment for ten dollars. The one person in five who will serve may be cognitively unlike the four who refuse. Moreover, the cognitive correlates of voluntarism may be different in different age groups. The proposed studies will be the same as in the original research plan, however, a payment variable will be introduced. We have determined through phone contacts that a forty dollars payment will reduce the attrition rate from 80 percent to less than 10 percent. We will use two samples of subjects: those who agree to serve for 10 dollars and those who will only serve for 40 dollars. The objective is simply to determine if the conclusions of the studies depend on the attrition rates. The project is well-suited to this purpose. It involves measures of several important kinds of cognitive activity -- retrieval, inference, and metamemory. All three activities are measured in the context of "ecologically valid" tasks resembling real-world functioning more closely than many laboratory paradigms. Each concerns the actualization of permanently-stored knowledge of the world. Three sets of studies are designed to suggest stable periods, peaks of points of decline in each of the three systems. Retrieval efficiency, expressed as a ratio of retrieved information to estimated data base, is studied in a question-answering task. Inference is studied by means of a sentence recognition paradigm and through recall of extended prose. Metamemory is studied in a "feeling-of knowing" paradigm. In the first study of each series, 10 dollars and 40 dollars groups will be included to ascertain whether the age functions depend on attrition rates.